Tanks Full or Empty during Offseason?
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Theory says warm moist air in your tank will condense on cold surface leading to water droplets. A full tank won't have any air to hold the moisture. In practice I have never noticed water in the racors during spring commissioning. I typically top off and do a thorough pump out in the fall. I do put biobore in the tank just in case.
Mostly empty - did not desire older fuel and never wanted an extra ton and a half of weight when on the hard.
Bkay
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I've had several boats over the years of various types and I've tried all the mainstream strategies. I don't feel there's a material difference between full, partially full, and empty. However, all else being equal I'm inclined to fill up before storage just because the fuel seems to be cheaper than in the following spring.
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I have 2 - 300 gallon steel diesel tanks. I never fill them completely since I only use about 250 to 300 gallons in a year. The tanks are 43 years old.
I leave around 50 gallons in the tank in winter. We use the boat 3 to 4 times during the winter.
I keep the engine room at a constant 50 degrees all winter so no damp air entering tanks.
My fuel tanks have sumps so any water will accumulate there to be pumped out.
I check for water monthly with KolorKut. No water ever found.
I open the inspection ports in the tanks every 5 years for a look and pump any debris out if found. I spray the sides of the tank with diesel with a wand and wash everything towards the sump where it gets pumped out, filtered and sprayed back out of the aimed wand.
I leave around 50 gallons in the tank in winter. We use the boat 3 to 4 times during the winter.
I keep the engine room at a constant 50 degrees all winter so no damp air entering tanks.
My fuel tanks have sumps so any water will accumulate there to be pumped out.
I check for water monthly with KolorKut. No water ever found.
I open the inspection ports in the tanks every 5 years for a look and pump any debris out if found. I spray the sides of the tank with diesel with a wand and wash everything towards the sump where it gets pumped out, filtered and sprayed back out of the aimed wand.
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nearly empty so the amount of old fuel will be minimal in spring. Then I only add as much as I will use soon so that I use up most of the old fuel in the first runs. Also because the fuel at the dock might be old if I am early.
I rarely full tanks unless Ill definitely be using it soon. Some sloshing around keeps stuff in suspension and low levels cause fuel return to increase the filtering rate for a little self polishing.
I rarely full tanks unless Ill definitely be using it soon. Some sloshing around keeps stuff in suspension and low levels cause fuel return to increase the filtering rate for a little self polishing.
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dhays
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That is the best reason I’ve ever read for either full or empty.
Of course, it is all academic to me. What is this “off season” of which you speak?
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I start watching diesel prices in March and when the price is low I buy fuel. There is usually a short period between the winter heating season and the summer vacation driving season where the fuel will be low - usually. Sometimes not.
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I agree.
I've been leaving diesel fuel tanks nearly empty during the winter season for over 20 years and have never found water in my tank. I do have the boat in a boathouse where the temperature is not extreme and no wind. That and engine room heat prevents the tanks from breathing in moist air.
jleonard
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Usually around 3/4 full. No particular reason, it's just what I do.
We have no offseason, so full.
Now when we lived on a lake in NC and had gas powered engines, we kept full for multiple reasons. First, condensation. Second, finding open marinas with fuel over the winter. Third, several marinas we wouldn't trust in the spring. Smaller marinas would frequently have water in their fuel for the first customers of spring. Not as bad as they once were. When I was a kid, tried to warn customers and speak to marina owners where I knew there were issues. Also, carried additives to try to help those with water in their tanks. 95% of the time it would work.
Comodave
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We usually have them full but this year ai am not going to fill them because I am going to replace my port tank so I want it as empty as possible. However there will still be at least 150 gallons that I will have to pump out.
dhays
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CMS is a member here. CMS is Rod Collins, a ABYC certified marine electrician. He posts on many forums as “Maine Sail”. He is an independent contractor who has provided boaters helpful advice for years as well as running his own marine services business in Maine.
I think Rod got tired of answering the same questions repeatedly but he has posted tons of articles on a variety of topics on his website www.marinehowto.com. I believe the article describing his fuel tank tests are on his website.
The website is a great resource. Rod also sells some gear from his website and I’ve found his prices to be very competitive, plus I much prefer to support someone who has given me, and so many others, excellent advice over the years.
I agree his website and tests are first class.
My only issue with his winter fuel tank test was it was empty so condensation could evaporate. I'd like to see it repeated w a partial fill of gas or diesel instead of empty. That way any condensation would be covered by the fuel and no / little opportunity to evaporate.
My only issue with his winter fuel tank test was it was empty so condensation could evaporate. I'd like to see it repeated w a partial fill of gas or diesel instead of empty. That way any condensation would be covered by the fuel and no / little opportunity to evaporate.
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Thanks Dave.
Lou_tribal
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For the last 4 years we are leaving the tank the way they are for winter, it was almost empty (less than 1/4 left), half empty, or almost full (3/4 full). Never seen any difference. No more or less water in the separator, no difference in fuel quality (or ability to burn), just no difference.
Not sure if keeping some fuel 4 to 6 months in a tank would make a difference. There are many diesel usage where fuel is kept more than 6 months sitting. Maybe some factors may make a difference but for now did not notice any.
L
Not sure if keeping some fuel 4 to 6 months in a tank would make a difference. There are many diesel usage where fuel is kept more than 6 months sitting. Maybe some factors may make a difference but for now did not notice any.
L
dhays
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I don’t have enough experience with “large” diesel fuel tanks. I’ve only had this boat for 3 1/2 years. Most of the time, my tanks are about 1/2 full. We use the boat all year, but obviously more in the warmer months. It is cool and wet here in the winter and the boat stays in the water all year. So far, I’ve never found any water in my Racors and I run all my fuel through one primary Racor 10 micron filter and a 2 micron secondary filter. My primaries are a darkish grey when they are changed. I don’t use any fuel treatment.
On my sailboats, I used even less fuel. On my last sailboat most years I would top off its 50 gallon tank in July. Not a plan, it just seemed to happen that way. Sometimes I would put some Stabil in the tank when I filled it up, but most of the time I would simply forget. Again, never any water or crud in the fuel despite the cold and wet winter months.
On my sailboats, I used even less fuel. On my last sailboat most years I would top off its 50 gallon tank in July. Not a plan, it just seemed to happen that way. Sometimes I would put some Stabil in the tank when I filled it up, but most of the time I would simply forget. Again, never any water or crud in the fuel despite the cold and wet winter months.
FF
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With a gas boat , and ethanol in the fuel,as empty as possible is best sine the first fill up will dilute the water grabbed by the ethanol.
On a diesel boat most modern filters will catch water , but they will also filter the asphaltene.
On old aged fuel , there could be enough ashphaltene to plug the fuel filters.
Add dead bug residue and you will understand why some folks install DP, differential pressure gauges at the helm that can monitor and alarm the fuel filters.
Asphaltene - Wikipedia
https://en.wikipedia.org/wiki/Asphaltene
The Murphy 0-15 PSI Mechanical Differential Pressure Swichgage 20DP-15 is a diaphragm-actuated, differential pressure-indicating gage with a built-in electrical switch. ... The gage pointer acts as a pressure indicator and as one switch pole which completes a circuit when it touches the adjustable limit contact.
Murphy-Murphy 0-15 PSI Mechanical Differential Pressure Swichgage ...
www.partdeal.com/murphy-0-15-psi-mechanical-differential-pressure-swich...
On a diesel boat most modern filters will catch water , but they will also filter the asphaltene.
On old aged fuel , there could be enough ashphaltene to plug the fuel filters.
Add dead bug residue and you will understand why some folks install DP, differential pressure gauges at the helm that can monitor and alarm the fuel filters.
Asphaltene - Wikipedia
https://en.wikipedia.org/wiki/Asphaltene
The Murphy 0-15 PSI Mechanical Differential Pressure Swichgage 20DP-15 is a diaphragm-actuated, differential pressure-indicating gage with a built-in electrical switch. ... The gage pointer acts as a pressure indicator and as one switch pole which completes a circuit when it touches the adjustable limit contact.
Murphy-Murphy 0-15 PSI Mechanical Differential Pressure Swichgage ...
www.partdeal.com/murphy-0-15-psi-mechanical-differential-pressure-swich...
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rgano
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My trawler spent four years under my ownership in San Diego and another 25 years here with me in the Florida panhandle. Boat and its 640-gallon capacity spread over four tanks tended to sit more in the winter months here. I never bothered about keeping tanks filled, and some winters they were relatively low. I never in all those years saw a drop of water in a Racor bowl, and all tanks were bottom drawn.
rslifkin
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Mine has been stored every winter with full tanks (gas) since it was built, both in water and on the hard at different points in time. About 13 of those years were with 10% ethanol gas, as that's all there was past a point in CT. Fuel was always stabilized at the last fillup and non-ethanol has always had drygas added before winter. Never had a fuel related issue in the spring.
Only ethanol issue we ever had was some fuel lines needing replacement due to not being ethanol compatible, but they were due for replacement due to age anyway. Tanks are aluminum, so no concern for ethanol dissolving them.
As far as ethanol and condensation, it can absorb a good bit harmlessly (while it would otherwise puddle in the tanks). It's only an issue if it absorbs enough to cause separation (which in one of my 210 gal tanks would require over a gallon of water to cause any separation at 10% ethanol).
Only ethanol issue we ever had was some fuel lines needing replacement due to not being ethanol compatible, but they were due for replacement due to age anyway. Tanks are aluminum, so no concern for ethanol dissolving them.
As far as ethanol and condensation, it can absorb a good bit harmlessly (while it would otherwise puddle in the tanks). It's only an issue if it absorbs enough to cause separation (which in one of my 210 gal tanks would require over a gallon of water to cause any separation at 10% ethanol).
